Hearing aid technology has progressed rapidly in recent years. Technological advancements in this field continue to improve the miniaturization, reception, wearing-comfort, life-span, and power efficiency of hearing aids. With these continual advances in the performance of ear-worn acoustic devices, ever-increasing demands are placed upon improving the inherent performance of the miniature acoustic transducers that are utilized. There are several different hearing aid styles known in hearing aid industry: Behind-The-Ear (BTE), In-The-Ear or All-In-The-Ear (ITE), In-The-Canal (ITC), and Completely-In-The-Canal (CTC).
Generally, a listening device, such as a hearing aid or the like, includes a microphone assembly, an amplifier and a receiver (speaker) assembly. The microphone assembly receives acoustic sound waves, and generates an electronic signal representative of these sound waves. The amplifier accepts the electronic signal, modifies the electronic signal, and communicates the modified electronic signal (e.g. processed signal) to the receiver assembly. The receiver assembly, in turn, converts the increased electronic signal into acoustic energy for transmission to a user.
A known receiver assembly comprises a housing, an armature, a drive rod, a pair of drive magnets, a diaphragm, a drive coil, a yoke, a sound outlet port, and an electrical terminal. The diaphragm is disposed within the housing, defining an output chamber and a motor chamber. The armature is disposed within the motor chamber and has an operative element comprising a fixed end and a movable end. The armature is coupled by the drive rod to drive the diaphragm. The drive magnet structure having a central passage surrounds the movable end of the armature and provides a permanent magnetic field within the passage. The drive coil is disposed about the armature and is located proximate to the permanent magnet structure.
To provide a magnetic flux, the drive magnet may be disposed within the magnetic yoke. The drive magnet may be made of a hard magnetic material, such as, for example, Ferrite, Alnico. The magnetic yoke may be made of Nickel-Iron. This arrangement of the magnet assembly (drive magnet-magnetic yoke structure) has several disadvantages. The hard magnetic material used in the drive magnet often has a relatively low energy content and further it requires a certain thickness to provide sufficient flux density. Moreover, the overall size of the magnetic yoke must be made large enough to avoid magnetic saturation. Also, the physical volume of the material places limits on the size of the receiver assembly making size reductions difficult.
Accordingly, there is a need for a transducer, for example a microphone or receiver that is inexpensive, simple to manufacture and scalable to relatively small sizes.